The present invention relates to a titanium alloy treatment process.
The process of the present invention comprises molding an .alpha.+.beta. titanium alloy and a .beta. alloy, subjecting the molded article to a .beta. solution treatment above the .beta. transformation point, quenching the treated article to room temperature to form a martensitic single phase or a .beta. single phase, subjecting the resultant article to an aging treatment below the .beta. transformation point to finely precipitate an .alpha. precipitate on the martensite phase or the .beta. phase, and then subjecting the article to a mirror finishing treatment to produce a mirror finish.
In general, an .alpha.+.beta. titanium alloy article is a two-phase alloy comprising a hard phase and a soft phase and has a difference in the hardness and the workability between the .alpha. phase and the .beta. phase. Therefore, even when a mirror finishing process is conducted, a mirror finish can not be furnished. Further, in .beta. titanium alloy article as well, an .alpha. phase is present although the amount thereof is small, which makes it impossible to prepare a mirror finish state due to a difference in the hardness and the workability between the .alpha. phase and the .beta. phase even when a mirror finishing process is conducted.
The conventional heat treatment of a titanium alloy article has been conducted for the purpose of enhancing the strength or toughness of the same as disclosed in Japanese Patent Publication No. 48025/1983 and Japanese Patent Laid-Open No. 281860/1986 wherein the article is solution treated below the .beta. transformation point, and quenched and aged below the .beta. transformation point. In such a treatment, a proeutectoid .alpha. phase remains and there exists a difference in the hardness and the workability between the proeutectoid a phase and the phase precipitated from the .beta. phase by the aging treatment. Thus, a mirror state can not be obtained even when a mirror finish finishing process is conducted.
Therefore, a titanium alloy article has been used in a satin finish state or after a surface treatment such as overcoating.
A titanium alloy has many advantages such as high specific strength, high temperature strength and good corrosion resistance and therefore has been extensively used for construction or mechanical parts. In these products, a heat treatment is conducted for the purpose of imparting various attributes such as strength, thoughness, corrosion resistance and vibration resistance. In the past, there had been no desire to create a mirror finish state. In recent years, however, these products have been used for ornaments by virtue of features of the titanium alloy such as small specific gravity, good corrosion resistance, high hardness and high-grade finish. In this case, a surface treatment has been used such as overcoating or in a satin finish pattern but this treatment does not produce a mirror finish.
The reason for this is as follows. In the titanium alloy, both a hard phase and a soft phase exist (cf. FIG. 1 (A)), so that, in the mirror finishing treatment, the soft phase is selectively polished (cf. FIG. 1 (B)), or otherwise the soft phase becomes broken and fallen (cf. FIG. 1 (C)). This causes an uneven portion to be formed on a finished surface, so that a satin finish pattern is formed and no mirror finish state can be achieved.